Seed-specific transgene expression is required for a number of applications utilizing genetic engineering. These include transgenic means to improve seed nutritional quality by manipulating flux through metabolic pathways (Hitz et al., 1995; Kinney, 1996; Shintani and DellaPenna, 1998; Goto et al., 1999) and for the production of novel compounds of industrial or pharmaceutical value (Cahoon et al., 2000) in a convenient package, the seed. Some of these transgenic traits may require expression of more than one transgene in the developing seed (Ye et al., 2000). In other cases, metabolic engineering to improve seed quality may require over-expression and/or suppression of various genes during seed development. Each step will require a promoter of appropriate strength depending on the desired degree of over-expression or suppression. In addition, a promoter with appropriate developmental timing may also be required. Even if the same degree of expression of more than one gene is required, it is not advisable to use the same promoter for multiple introduced genes. In some cases of high copy number integration of transgenes, promoter homology can lead to gene silencing (Vaucheret, 1993; Brusslan and Tobin, 1995; Park et al., 1996).
Seed storage proteins are expressed at high levels during seed development, and their expression is tightly controlled both spatially and temporally in the developing seed. Therefore, regulatory sequences from genes encoding seed storage proteins represent a valuable source of promoters that can be utilized to drive the expression of transgenes in a seed-specific manner. The promoters from soybean β-conglycinin genes (Barker et al., 1988; Chen et al., 1988; Lessard et al., 1993), French bean phaseolin gene (Bustos et al., 1989, 1991; Kawagoe et al., 1994), sunflower helianthinin gene (Bogue et al., 1990; Nunberg et al., 1995), and the carrot Dc3 promoter (Seffens et al., 1990; Kim et al., 1997) are examples of some of the well-characterized seed-specific promoters from dicots. Despite this array of other promoters available, the problems of expression levels and gene silencing are still an issue. Thus, it is clear that there will be an increasing need for promoters of varying strengths from more than one source to meet the future demands to regulate expression of one or more transgenes in seeds.